A wireless local area network (LAN) has advantages including that space for cables is reduced, and a mobile terminal including a notebook personal computer (notebook PC) can be connected to a LAN without losing the mobility, over a wired LAN. In addition, since a high speed and low cost are implemented in the wireless LAN, the practical use of the wireless LAN is further accelerated. Based on such situations, the standardization of the wireless LAN has been worked by Institute of Electrical and Electronics Engineering (IEEE).
Particularly, in a radio packet communication system that is represented by a wireless LAN, there is a problem of a contention for wireless resources between a plurality of terminals. In order to avoid the contention for wireless resources, a medium access control (MAC) is necessary. As an MAC protocol for the wireless LAN, a carrier sense multiple access (CSMA) system has been proposed in which a terminal detects a carrier of the other terminals before transmission of a packet, which is called carrier sense, and transmits a packet in a case where the carrier is not detected. In addition, a carrier sense multiple access with collision avoidance (CSMA/CA) system has been also proposed in which a packet collision avoiding structure is added to the CSMA system.
The CSMA/CA system is a system in which communication is initiated, the communication is assumed to be successful in a case where a reply of an acknowledge (ACK) signal is received from a wireless node of a communication partner, and the occurrence of communication collision with another wireless node is assumed, and packet data is retransmitted by arranging a back off time in a case where an ACK signal is not received.
Particularly in recent years, there are many CSMA/CA systems that are in compliance with the IEEE 802.15.4 standard. The IEEE 802.15.4 standard is for wireless communication using a frequency near 868 MHz, 915 MHz, and 2.45 GHz and is particularly used for a home appliance-dedicated local area network such as Zigbee (registered trademark). In Zigbee (registered trademark), a PHY layer and an MAC layer defined in the IEEE 802.15.4 standard are used, and a network layer and an application layer, which are uppers layers thereof, are standardized. Zigbee (registered trademark) enables realization of ultra-low power consumption, miniaturization, and low cost by utilizing the features of the IEEE 802.15.4 standard.
As above, the IEEE 802.15.4 standard has attracted attention as a key technology for realizing not only a sensor network but also a home network, an office network, and a communication network for communicating with various medical apparatuses installed to a human body and for realizing a ubiquitous network society in the future.
Generally, according to wireless communication that is compliant with the IEEE 802.15.4 standard, as illustrated in FIG. 15, local area wireless communication is performed between a network coordinator (NC) 71 that controls a network 7 and a plurality of end devices (ED) 72. In addition, as an example of the network 7, a variety of network forms such as a star type, a tree type, and a mesh type can be selected.
In addition, in the wireless communication that is compliant with the IEEE 802.15.4 standard, a so-called super frame structure using a beacon is used. In the super frame structure, a beacon interval is divided into a contention access period (CAP) during which all the EDs 72 can perform access, a contention free period (CFP) during which a specific ED 72 can exclusively perform access, and an inactive period during which access of all the EDs 72 is prohibited. In addition, the CFP is equally divided into seven parts through a guaranty time slot (GTS) mechanism and can be allocated to EDs 72 for which communication is desired to be performed with high priority.
As conventional radio packet communication systems that are compliant with the IEEE 802.15.4 standard, for example, systems disclosed in Patent Literatures 1 and 2 and the like have been proposed. In addition, as a technique for suppressing the collision of packets in the CSMA/CA system to a minimum level, for example, techniques disclosed in Patent Literatures 3 and 4 have been proposed.